The present invention relates to a method of controlling and regulating the traveling speed of a continuous cigarette rod on a cigarette manufacturing machine.
On cigarette manufacturing machines, a continuous strip of paper is fed on a conveyor belt through a loading station where a stream of shredded tobacco is deposited on to the strip. The strip is then folded transversely about the tobacco to form a continuous cigarette rod, which is fed on the conveyor belt to a transverse cutting head.
A major problem for ensuring correct operation of known machines of the aforementioned type is that of so controlling the paper strip, and consequently the conveyor belt, that the traveling speeds of both are substantially constant and equal to a predetermined speed depending on the substantially constant rotation speed of the cutting head by which the continuous rod is cut into a succession of portions of, at least theoretically, the same length. Any departure, in fact, in the traveling speed of the strip from said predetermined value results in the rod being cut into portions of other than the required length.
In connection with the above, it should be pointed out that, on known machines of the aforementioned type, the conveyor belt is looped about a number of transmission pulleys and a drive pulley, and that any departure in the traveling speed of the belt from said predetermined value is mainly caused by gradual wear of the drive pulley and, consequently, for a given angular speed, by a gradual reduction in its-surface speed.
On known machines of the aforementioned type, the traveling speed of the paper strip is controlled by making and subsequently detecting relatively small marks on the strip, which, by means of a mark counting device, enable the traveling speed of the strip and, consequently, the conveyor belt to be determined substantially accurately, and any departure from said predetermined value to be accordingly eliminated.
The above known control method, however, fails to cater for relatively high-speed strips, in which case, vibration of the machine and the relatively limited time available for detecting the marks on the strip invariably result in reading errors and, consequently, misadjustment, thus jeopardizing correct operation of the machine.